solid state relay

[doug]

   Can anyone tell me if I can replace my electromagnetic relay with a solid state relay? Will there be any issues? My heat  controller is a TCG612. I'm on my third relay and wanting to improve the dependability of my set up. Thanks

[Russ]

Greetings Doug!  I would sure think it would be possible.  What is the trigger voltage for your current relay and is it AC or DC?  SSR's have a pretty wide control voltage range.  For example, the ones I have laying on my desk work with 3 to 32VCD for their control voltage.  They also make ones that trigger off of AC if you need.  Also, what is the load voltage and current?

A while back I built a sump pump controller with an arduino board.  We live in a very wet area and all of the commercially available controllers and switches kept wearing out, so I built my own with components I knew I could replace if they went bad.  Of course the mechanical relay was the weak spot.  After going through 2 mechanical relays in a short time, I knew I needed to move to an SSR.  After installing the SSR I haven't had to touch it since.  Your reliability will certainly increase.

[doug]

Hey Russ,
 The relay is 120vac. It's the relay that operators the 500w heater cartridge in the preheater block that is activated from the PID heater controller.

[Russ]

Ahh yes, so very similar to what I have going on I would imagine.  Reply #5 shows what I am using for my relay:
http://wasteoilheaterforum.com/index.php?topic=208

I'm a fan of Opto 22 SSR's.  They have always worked well for me and they are made in the USA.

My PID has an SSR output, so it supplies 12VDC to the SSR which turns the cartridge heater on and off.  I see that the instructions for my PID also list a model that outputs AC for the use with a mechanical style relay.  So are you saying that your PID is sending 110VAC to the relay for turning the relay on and off?  If so, I would think any of these should work:
http://www.opto22.com/site/pr_selector.aspx?cid=3&qs=10061016#1052

Check ebay for the part numbers.  I have had good luck finding brand new relays at good prices.

[doug]

Russ, Thanks for the info.

[doug]

I see these ss relays mounted on heat sinks. Would I need to use a heat sink or mount it where my old relay had been?

[Russ]

I don't have heat sinks on mine currently, but I am thinking of adding them.  I actually have 2 SSR's in my system.  One controls the cartridge heater and the other controls the small compressor and blower motor.  I haven't ever had a problem with the cartridge heater relay, but I have with the other.  I suspect its because it is a continuous load rather than the intermittent load from the cartridge heater. 

What happens is that when the water reaches high temp, the aquastat cuts power to the cartridge heater and when the block drops below 200 degrees, the alarm contacts on the PID open and shut the relay off that controls the compressor and blower motor.  If it's cold out and the boiler starts again soon after it shut down, the relay is still hot and wont provide full current to the compressor and blower motor causing the system not to start.  If I jump the terminals with a wire, the system will start and run fine, but it's the initial start up that doesn't work.  If the system cools down more, then it has no problem starting again, so its definitely a heat problem.

You probably wouldn't have a problem just running the cartridge heater, but heat sinks are cheap and if you have room for it, it certainly wont hurt.